Orthodontic brackets have long been used for applying corrective forces to teeth. Typically an orthodontic bracket comprises a tooth bonding surface and a slot for receiving an archwire which transmits corrective forces from the archwire to the tooth. Generally, orthodontic brackets of the prior art are made of a metal so as to provide sufficient strength for the transmission of these forces to the teeth. An individual undergoing orthodontic treatment generally has a considerable number of these brackets applied to his or her teeth. Individuals generally consider these orthodontic brackets as being extremely unsightly in appearance.
It is long considered desirable by manufacturers of orthodontic brackets to provide a bracket which is less sightly in appearance. One solution suggested was the use of clear plastic materials, however, these materials have been found to have insufficient strength for transmitting the appropriate forces to the teeth. In order to avoid this problem metal supports or inserts have been suggested for use with plastic. However, this then suffers from the same unsightly problem that total metal brackets present, however, maybe now to a certain lesser degree.
There has also been suggested use of single crystalline alumina material for an orthodontic bracket as described in U.S. Pat. No. 4,639,218 to Jones et al. and U.S. Pat. No. 4,595,598 to DeLuca et al. In U.S. Pat. No. 4,639,218 there is described an alpha alumina orthodontic bracket which is made by a seed crystal which is pulled from molten alumina by a die having a cross-sectional configuration substantially identical to that of the orthodontic bracket. After the crystal is drawn it forms a rod which is cut into a plurality of individual brackets by known cutting/grinding techniques. A problem with this type of method is that it is relatively expensive and is limited to the configurations that ray be applied to the top surface of the bracket. Additionally, and perhaps more importantly, the grinding and cutting technique used to form the final configuration results in sharp edges which may cause damage to the tissue and introduce stresses in the product which may later cause failure of the bracket
Another problem associated with orthodontic brackets made of single crystalline material, also recognized by the '218 reference, is the ability of the material to adhere to the surface of a tooth. The '598 reference to De Luca et al. discloses two ways whereby adhesion is improved between the bracket and tooth. In one method a small undercut is provided at each side edge of the bonding base. A problem with this method is that it requires a grinding operation which can introduce serious surface flaws to the very brittle crystalline material.
In the second method a siliceous layer is applied to the bracket and then a silicone coupling agent is applied to the bracket which has an affinity for the siliceous material A problem associated with this method is that great care is required in placing of the siliceous layer on the bracket and applying the cement. Any contaminations on any of the surfaces could substantially reduce the adhesion of the cement to the siliceous layer. Additionally, the shelf life of the coupling agent can have an adverse affect on the adhesive bond formed.
Applicants' have developed an improved orthodontic bracket and method of making same which minimizes or eliminates the problems of the prior art.